Tee Capistrano3's logs to stdout and a log file.

tee_capistrano_log.rb

before :deploy, :setup_tee do
  require "tee" # tee gem
  
  # root is where Capfile is placed.
  root = File.dirname(File.expand_path(Rake.application.rakefile))
  path = File.join(root, "log/deploy_#{release_timestamp}_#{local_user}.log")
  FileUtils.mkdir_p(File.dirname(path))
  file = File.open(path, "w").tap { |f| f.sync = true }

  formatter = SSHKit.config.output
  org = formatter.instance_variable_get(:@original_output)

  tee = Tee.open(file, stdout: org)                                                                                                                                                                                             
  formatter.instance_variable_set(:@original_output, tee)
end

もしかして、単に stdout = $stdout; $stdout = Tee.open(file, stdout: stdout)すれば良かっただけ？
→ $stdoutがFormatterの初期化前に渡される必要があるので、微妙そう。